Rough idle / Bank 1 too lean / Bank 2 too lean

[proradvlx]

Wondering if anyone has come across this in with their vehicle.

First, history: 2004 Explorer XLT 4door AWD 4.0L V6 Flex Fuel

Noticed slight rough idle at or below 1000rpm - above 1000, no problem. Then started getting the "Service Engine Soon" light, and when running the codes would get either " Bank 1 too lean " or " Bank 2 too lean ", or both.

Here's what I've already replaced, in the order replaced:

1. Both upstream/pre-cat oxygen sensors ( Motorcraft parts )
2. Both downstream/post-cat oxygen sensors ( Motorcraft parts )
3. Fuel filter ( Motorcraft part )
4. Mass air flow sensor.

Just did the MAF today - started the engine, started up fine, smooth, then idled down.... and got to about normal idle rpm, started feeling the rough idle. So none of the changes seem to have an effect, and I'm running out of ideas. The only other thing I can think of is the fuel pump....... but it's OK above 1000rpm, and I'm REALLY hoping it's not the fuel pump.

So, any way to check the fuel pump at or below 1000rpm, or any other ideas you could throw at me, I would greatly appreciate it!! Thanks!

 

[J_C]

I'd hook up a scan tool capable of live data and look at long term fuel trim.

You might have a vac leak, possibly the intake manifold, or a hose, or dirty/bad IAC valve.

It is unlikely to be the fuel pump/fuel-pressure. That would have more effect at higher load rather than idle but a scan tool should show the fuel pressure if you don't have a valve on the fuel rail to hook a pressure gauge up to.

 

[SyberTiger]

Wondering if anyone has come across this in with their vehicle.

First, history: 2004 Explorer XLT 4door AWD 4.0L V6 Flex Fuel

Noticed slight rough idle at or below 1000rpm - above 1000, no problem. Then started getting the "Service Engine Soon" light, and when running the codes would get either " Bank 1 too lean " or " Bank 2 too lean ", or both.

Here's what I've already replaced, in the order replaced:

1. Both upstream/pre-cat oxygen sensors ( Motorcraft parts )
2. Both downstream/post-cat oxygen sensors ( Motorcraft parts )
3. Fuel filter ( Motorcraft part )
4. Mass air flow sensor.

Just did the MAF today - started the engine, started up fine, smooth, then idled down.... and got to about normal idle rpm, started feeling the rough idle. So none of the changes seem to have an effect, and I'm running out of ideas. The only other thing I can think of is the fuel pump....... but it's OK above 1000rpm, and I'm REALLY hoping it's not the fuel pump.

So, any way to check the fuel pump at or below 1000rpm, or any other ideas you could throw at me, I would greatly appreciate it!! Thanks!

Idle Air Control (IAC) valve?

 

[SyberTiger]

And THIS THREAD may be applicable even though your engine is the 4.0 and not the 4.6.

 

[410Fortune]

4.0 leaking intake o rings will cause lean both banks

 

[Mymeatb18]

I had a bad fuel pump causing this same issue and it sure as hell didn't feel like it and cuz I was getting poor gas mileage. I basically changed everything you can think. Probably was a good idea anyways but ended up being the fuel pump.